The present invention relates in general to a printing blanket construction, and more particularly, to an improved printing blanket which reduces printing gap, which reduces the impact forces on the leading edge of the blanket, and which prevents the penetration of ink, solvents, moisture and the like into the blanket plies during use.
One of the most common commercial printing processes is offset lithography. Non-tensioned offset printing blankets are typically made on a thin, low elongation carrier, or backing, having ends that extend beyond the end of the actual printing blanket. The ends are bent or otherwise formed so that they can be inserted into a narrow-gap printing press cylinder lock-up to hold the blanket in place.
However, this type of narrow-gap lock-up system results in the leading and trailing end edges of the blanket being exposed rather than tucked inside the lock-up or cylinder. This exposure subjects the blanket ends to mechanical impact forces and the penetration of water, inks and chemicals used during the printing process, which can result in swelling and delamination of the blanket layers. Such conditions may contribute to premature blanket failure.
A common method of avoiding this problem is to apply a sealant to the end edges of the blanket to prevent moisture from penetrating the layers. See, for example, Castelli et al., U.S. Pat. No. 5,749,298. However, as the blanket comprises a composite of dissimilar materials, many sealants do not adhere well to the dissimilar materials at the blanket edges, particularly due to the minimal surface area of the edges to which the sealant is adhered.
As an alternative to the use of sealants, attempts have been made to reduce the gap between the blanket ends when the blanket is attached to the cylinder. See, for example, U.S. Pat. No. 4,635,559, which teaches a blanket including a filler portion which is fixed to the end of the blanket and spans the gap between the leading and trailing edges. See also U.S. Pat. No. 5,732,630, which teaches a rubber blanket having leading and trailing edges including closures which interlock to form a seamless blanket when the blanket is placed on a blanket cylinder. However, such blanket constructions require the use of additional elements or filler materials which add to the cost of producing the blanket.
Accordingly, there is still a need in the art for an improved method of reducing printing gap and effectively protecting the leading edge of the blanket from impact forces and the penetration of moisture into the layers of the blanket construction.